Download External ear

EAR
EAR
• It consists of the auditory apparatus and the
organs concerned with balance which record
both rotary movements of the head and the
direction of the gravitational field acting on it.
• Ear is divided into three parts:
1. External ear (outer ear)
2. Middle ear
3. Internal ear (inner ear)
1. EXTERNAL EAR
• It consists of the auricle and the external
acoustic meatus.
• The auricle collects the sound waves, and the
external acoustic meatus transmits them
medially to the tympanic membrane, which
separates the external ear from the middle
ear.
External acoustic meatus
(external auditory meatus)
• It runs medially with a slight anterior
inclination.
• It is almost exactly in line with the internal
acoustic meatus, and their shadows are
superimposed in a true lateral radiograph of
the skull.
• It is approximately 24 mm. long, of which the
medial 2/3 is the bony part and the lateral 1/3
is the cartilaginous part.
• The skin of the cartilaginous portion contains
many ceruminous glands (which
produce cerumen, or earwax) and hairs.
• In the bony part of the canal the skin has no
hairs and few if any glands.
• Its diameter is not uniform; the narrowest
point is called the isthmus which is about 5
mm. from the tympanic membrane.
Tympanic membrane
(ear drum)
• Is an elliptical disc which is stretched across
the medial end of the external acoustic
meatus, and forms the greater part of the
lateral wall of the middle ear cavity.
2. MIDDLE EAR
• It is a narrow chamber whose cavity (the
tympanic cavity) lies between the tympanic
membrane and the lateral wall of the internal
ear, and communicates with the nasal part of
the pharynx through the auditory tube
(Eustachian tube).
• Three small auditory ossicles (malleus, incus,
and stapes) lie in the middle ear, and stretch
across it from the tympanic membrane to the
lateral wall of the internal ear to transmit the
vibrations of the tympanic membrane to the
internal ear.
3. INTERNAL EAR
• It consists of a complex system of
communicating cavities (the bony labyrinth)
situated in the densest part of the petrous
temporal bone.
• It contains a similarly shaped (to the bony
labyrinth), but narrower complex of
membranous tubes and sacs which constitutes
the membranous labyrinth, and on which the
sensory nerve fibers of the vestibulocochlear
nerve end.